Contrast agents are useful for ultrasound imaging because their presence can preferentially enhance scattering from regions of tissue depending on disease state. Therefore, the important element of contrast agent detection is the sensitivity of the detection scheme to echoes from contrast agent relative to echoes from tissue. We refer to this sensitivity to contrast echoes versus tissue echoes as specificity.
High specificity to contrast agents can be achieved in two ways: by exploiting the greater nonlinear response of contrast agents over tissue, particularly to low amplitude pulses, or by detecting modification (destruction, for example) of the contrast agent by an acoustic wave (the loss of correlation or LOC effect). (Tissue is not modified by the passage of an acoustic wave at diagnostic power levels.) This specification describes a technique called Contrast Pulse Sequence (or CPS) imaging that improves the specificity of contrast agent detection when the nonlinear response of the agent is used to distinguish contrast agent from tissue, maintains sensitivity to contrast agent when the LOC effect is used, and improves rejection of signals from moving tissue, which can corrupt the contrast agent signals.